The usual difference between non-transparent soaps and transparent or translucent soap lies in the crystallization of the finished soap product. Non-transparent soaps will normally solidify from a hot fluid state to a crystal conglomerate, which contains more or less soap in a colloidal dispersed state. On the other hand, translucent soap is made by keeping the crystal size of the soap bar small or by inhibiting crystallization of the soap during solidification of these bars.
In the past, translucent soaps were prepared by incorporating clarifying agents such as lower alkanols (soap crystallization inhibitors) and the soaps were framed, not milled and plodded. Subsequently, it was discovered that milled and plodded translucent soaps could be made by a variety of methods including careful regulation of electrolyte content, utilizing resin soaps, employing potassium soap, controlling moisture content, and utilizing specialized soap formulas. Also, careful control of the working of particular formulas and energy added to them during the processing was found to be useful in some cases in making translucent soap tablets by a process which included plodding of the soap and pressing of lengths cut from an extruded plodder bar.
For example, in U.S. Pat. No. 2,005,160 a natural resin is used in the production of a translucent soap bar and the process required spreading the hot fluid kettle soap in a thin layer and cooling that layer to room temperature, ie. specifically, it is stated that the soap is chilled to about 20.degree. C.
Although prior art shows that translucent and transparent soap bars could be made, the processes and the product were too often unsatisfactory. For example, crystallization inhibitors often made the soap malodorous or adversely affected the soap's tactile properties. The additives tended to evaporate in the process of making the translucent bar and therefore caused the product to lose its transparency. Some crystallization inhibitors caused the development of hard specks in the soaps, while others made the soap mushy or liable to slough excessively when it became wet, as when standing in a soap dish with water in contact with the cake bottom. When certain working conditions were required to produce a transparent soap via milling, plodding, and pressing, the processes employed would often take too long to be economical, or the process control would be too critical, so that excessive scrapping of off-specification product would result.
Today, it is generally accepted, that translucent soap can be made by keeping the crystal size of the finished soap bar small through either the use of new crystallization inhibitors or by use of high shear extrusion, that requires expensive and specialized equipment, to break down the crystal size. For example, in U.S. Pat. Nos. 3,793,214 and 3,864,272, glycerine and polyethylene glycol are added to the soap to promote translucency. Other well known additives include lanolin, sorbitol, and ethanol, to mention only a few.
Although translucency is difficult to achieve in a soap bar without additives or use of specialized equipment, high moisture translucent soap bars are rarely produced, since high moisture content in soap bars tends to make these bars soft. High moisture soaps are commercially available today. However, these soaps are either opaque or in the form of laundry soaps, which are often soft, nonmachinable, and not very translucent.
It is therefore, an object of the present invention to provide a process for the manufacture of translucent, high moisture soap bars.
It is a further object of the present invention to produce high moisture, bars translucent soap bars, without special additives or by using specialized equipment.
It is a still further object of the present invention to produce a translucent, hard soap bar at a moisture content between 18-279.